The present invention relates to a fish meal manufacturing system. Fish meal is presently manufactured generally in the following manner:
Raw fish is fed from a hopper continuously in a limited quantity, and is cooked by steam in a cooker. Then, after separation of almost all boiled liquid the cooked material is pressed for the further separation of pressing water. Fish cake produced by press moisture removal is dried in a dryer, and is ground to produce fish meal. Boiled liquid and pressing water are mixed to produce a fluid (called press water), which is fed at a suitable temperature to a separator. The fluid mixture is separated into fish oil, fish solubles, and wet fish meal.
Prior-art processing systems are not of a closed type and the foul gases produced in such systems are discharged into the atmosphere at any point where a solid material must be carried to subsequent processing equipment. Furthermore, not much emphasis is placed upon cleaning-up of foul gases and polluted water. This results in severe environmental problems caused by offensive odors and water pollution in regions where plants under conventional systems are operated.
Still further, on existing processing systems, raw fish which can rapidly lose its freshness are continuously fed from a hopper in limited quantities. Such systems are not conducive to obtaining quality products. The quality of the various kinds of products cannot be kept consistantly high from the start to finish of the operation. Raw fish kept for a relatively long time for use at the end of the operation must naturally be less fresh. Thus products of poor quality, which may be even harmful, are quite commonly manufactured in conventional plants. However, this fact of lessened quality is not sufficiently recognized.
Generally, a cooker for boiling raw fish is a horizontal type cylindrical device which is slightly slanted and is enclosed with a steam jacket for heating the raw fish in the cooker. In the long cylindrical cooker a given quantity of fish material is pushed and moved therethrough at a constant speed, for example by means of a screw conveyer, which is provided inside the cooker. During this time the fish material is boiled in situ solely with the heat which is conducted through the steam jacket covering the cooker body, without any additional material, such as hot water, being added. The raw fish, upon completion of boiling, is discharged from the cooker so as to be fed to the next processor.
Boiling raw fish is a heat processing method in which the raw fish is heated in such a manner that substances constituting the fish body, particularly the fish meat, are contracted and water and fish oil contained therein are extracted. The fish meat is thus converted into a material which is easy to digest and is a good feed for animals.
In the case as described above, the fish body is boiled for a given period to extract relatively small quantities of hot water and fish oil. Boiling is continued in the extracted liquids, but the hot water present is insufficient to boil the entire fish body evenly and satisfactorily, and consequently the effect of boiling cannot be produced uniformly. In addition to this disadvantage, the fish body is formed in a layer, which is moved at a fixed speed in the cooker and is not stirred vigorously, as the cooker is not designed for such operation. As a result, the fish body within the core of the cooker cannot be heated as is the portion of the fish body which is held in contact with the inner wall surface of the cooker. In other words, a conventional cooker cannot be employed satisfactorily for evenly boiling the fish body or the fish meat feed material owing to defects in such boiling process and in the design of the cooker. Furthermore, it is noted that such a cooker is not based on the principle of boiling the entire fish body. Rather, emphasis in the prior art is placed on the in situ processing of raw fish with external heat applied to the fish body and on the theory and results of such heating.